Background: Japanese hop is an important cause of weed pollinosis in East Asia. Its
pollen is abundant in autumn. This pollen is known to be the cause of many allergic diseases. However,
molecular characteristics of its allergens have not been elucidated.
Objective: In this study, we produced recombinant proteins of allergen homologues from Japanese
hop by the analysis of expressed sequence tags (EST), and evaluated its allergenicity.
Methods: cDNA library was constructed using as little as 50 ng of total RNA from Japanese hop
pollen. Allergen homologues were identified by the initial screening of 963 EST clones. Recombinant
proteins were overexpressed in the E. coli expression system and purified using Ni-nitrilotriacetic
acid-agarose. Purified proteins were analyzed by ELISA.
Results and Discussion: Japanese hop pathogenesis-related 1 protein (PR-1) shares 37.0 to 44.4%
of amino acid sequence identity with Art v 2, Cuc m 3, and Cyn d 24. Pectin methyl esterase (PME)
shows 23.2 to 50.2% of identities to Act d 7, Ole e 11, and Sal k 1. Polygalacturonase (PGs)
shows 16.7 to 19.3% of identities to Phl p 13, Cry j 2, Cha o 2, Jun a 2, Pla a 2, and Pla or 2. IgE
antibodies from Japanese hop allergy patients’ sera recognized PR-1 (3.4%), PME (13.8%), PGs
(3.7%), and profilin (13.8%), respectively.
Conclusion: Novel allergenic components were identified, even though low IgE reactivity was displayed
reflecting the low degree of cross-reactivity with other pollen allergens. We believe that these
molecules have worth further studies.